Electrical power apparatus

ABSTRACT

Electrical power apparatus, such as a transformer, electrical reactor, or a circuit breaker, having a casing containing fluid cooling means, and at least one electrical lead immersed in the fluid cooling means. The magnitude of the electrical stress is reduced about the electrical lead, without impeding the removal of heat from the lead by the fluid cooling means, by disposing a spirally wound electrode about the electrical lead, and connecting the electrode to the lead.

3,668,584 1451 June 6, 1972 1541 ELECTRICAL POWER APPARATUSMeissner................................ l 74/ l 27 [72] Inventors:l-larra] T. Robin, Muncie; Virgil L. B082, FOREIGN PATENTS 0RAPPLICATIONS Daleville, both of lnd.

639,040 6/1950 Great Britain.........................

[73] Assignee: Westinghouse Electric Corporation, Pittsburgh,Pa.

Primary Examiner-Thomas J. Kozma Attomey-A. T. Stratton, F. E. Browderand D. R. Lackey [22] Filed: Apr. 13, 1971 [57] ABSTRACT Electricalpower apparatus, such as a transformer, electrical reactor, or a circuitbreaker, having a casin [2]] Appl. No.:

g containing fluid cooling means, and at least one electrical leadimmersed in the fluid cooling means. The magnitude of the electricalstress is reduced about the electrical lead, without impeding theremoval of heat from the lead by the fluid cooling means, by disposing aspirally wound electrode about the electrical lead, and connecting theelectrode to the lead.

UNITED STATES PATENTS 1,691,329 11 1928 Austin 174/127 14Claims,6Drawing Figures IIIIIII I ELECTRICAL POWER APPARATUS BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates in general toelectrical power apparatus, such as high voltage power transformers,electrical reactors, and power circuit breakers, and more specificallyto structures for reducing the potential gradient about certain portionsof such apparatus, while promoting heat removal from these portions. 2.Description of the Prior Art The trend to higher and higher electricaltransmission voltages has introduced special stress control problems inrelated electrical power apparatus, such as power transformers, shuntreactors, power circuit breakers, and the like. Stress control abouthigh voltage leads disposed directly in the fluid cooling medium of suchapparatus is especially troublesome, as present methods of controllingthis stress create other problems, the solution to which adds to themanufacturing cost of the apparatus. Examples of such high voltageelectrical leads are the electrical leads connected to the bushings intransformers, reactors, and power circuit breakers, tap leads connectedbetwe'entransformer coils and a tap changer, and connections betweencoil groups of a power transformer. Care must be taken in the design ofsuch apparatus to insure 'that the electrical stress surrounding theseleads does not exceed the electrical breakdown strength of thesurrounding fluid cooling dielectric, which is usually mineral oil.

The usual prior art arrangements for lowering the magnitude of theelectrical stress surrounding such leads to values below the breakdownstrength of the mineral oil consists of wrapping the leads heavily withcellulosic insulation, such as crepe paper. Crepe paper has a higherdielectric strength than mineral oil, and can thus withstand the highelectrical stress immediately adjacent to the conductive portion of theelectrical lead, and it has a higher dielectric constant than mineraloil, and is thus not as highly stressed as mineral oil would be in thesame location. Further, the crepe paper insulation spaces the mineraloil from the lead, reducing the magnitude of theelectricalstress at thecrepe paper-oil interface.

While this prior art arrangement solves the stress problem, it createsother problems which add to the manufacturing cost of the apparatus. Theamount of crepe paper tape required is substantial, and the thickness ofthis layer of crepe paper tape increases with the voltage level of thelead. Thick layers of paper on theelectrical leads lower heatdissipation from the lead into the surrounding cooling medium, causingthe lead to operate at higher temperatures than permissible. ,Apredetermined maximum hot-spot temperature must not be exceeded, or thecrepe paper tape will deteriorate rapidly.

The reduced effectiveness of the leads in dissipating their FR lossesdue to the thick insulation layer has led to the adding of additionalconductive strands to the leads, in order to reduce the magnitude of theIR losses, and thus reduce the temperature of ,the lead structure. Thispractice, however, is often partially or wholly self-defeating, as theinsulated leads are usually disposed in areas of high leakage fluxfields, which may createcirculating current losses which offset thereduction in IR losses. Further, adding additional conductive strands tothe leads, and heavy layers of paper tape is undesirable, due to theresulting increased labor and material costs.

Thus, it would be desirable to provide new and improved electricalinductive apparatus having means for reducing the magnitude of theelectrical stress surroundi g high voltage electrical leads disposed insuch apparatus, which is less costly than prior art stress reducingstructures, and which maintains lead temperatures within acceptablelimits.

SUMMARY OF THE INVENTION Briefly, the present invention is new andimproved electrical power apparatus, such as power transformers,electrical reactors, and power circuit'breakers, of the liquid filledtype. The

magnitude of the electrical stress surrounding vat least one electricallead disposed in such apparatus is reduced by disposing an electrodeabout the lead, with the electrode having a larger effective radius thanthe lead. The electrode is formed of an electrical conductor having a.plurality of spiraled turns, which turns encircle the lead and arespaced therefrom by spacer means. The electrical conductor of theelectrode is connected to the electrical lead, to reduce the potentialgradient between the lead and surrounding spaced electrode tosubstantially zero. Thus, heavy taping of the electric lead is notrequired and the FR losses produced in the lead are readily dissipatedinto the surrounding liquid coolant. Since the effectiveness of theresulting structure is increased, the potential gradient adjacent theelectrode is reduced. Since the electrode carries no current, and thushas no IR losses, its effectiveness may be increased by applying solidinsulation about its turns, without regard to impeding the heattransfer. The spiraled turns of the electrode allow free flow of theliquid coolant both through the opening defined by the turns,

the turns of the spiraled electrode.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be betterunderstood, and further ad vantages and uses thereof more readilyapparent, when considered in view of the following detailed descriptionof exemplary embodiments, taken with the accompanying drawings, inwhich:

FIG. 1 is a perspective view, partially cut away, of a liquid filledtransformer which may utilize the teachings of the invention;

FIG. 2 is a fragmentary elevational view of a bushing lead includingstress reducing means constructed according to the teachings of theinvention;

FIG. 3 is a cross-sectional view of the bushing lead and stress reducingmeans shown in FIG. 2, taken along the lines Ill-III;

FIG. 4 is a fragmentary view of intercoil connecting leads having stressreducing means constructed according to the teachings of the invention;

FIG. 5 is a fragmentary view of a tap lead having stress reducing meansconstructed according to the-teachings of the invention; and v FIG. 6 isa fragmentary view of a lead and stress reducing means constructedaccording to still another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, andFIG. 1 in particular, there is shown a transformer 10, partiallycutaway, of the type which may utilize the teachings of the invention.While the transformer 10 is illustrated as being of the shell-form type,it is to be understood that it may be of the core-form type, and itbroadly represents high voltage liquid filled power apparatus havingelectrical leads therein which require special attention from theviewpoint of stress control. Transformer 10 includes a tank 12 filled toa level 14 with a fluid cooling means, such as mineral oil, and amagnetic core-winding assembly 16 disposed in the tank and immersed inthe fluid cooling means. The mineral oil aids insulating the electricalwindings from ground, and from one another, and it cools the magneticcorewinding assembly 16 by circulating upwardly therethrough, either byforced circulation, or by the natural thermal siphon efiect, with theheated oil being cooled by heat exchangers (not shown), which areconnected to the tank, in communication with openings 18 near the top ofthe tank 12, and pipes 20 near the bottom thereof. The oil circulatesupwardly through cooling ducts disposed in the magnetic core-windingassembly The magnetic core-winding assembly 16 of transformer 10, whichmay be single or polyphase, includes a winding assembly 24 and amagnetic core assembly 26. The winding assembly 24 includes a pluralityof high and low voltage coils which encircle leg portions of themagnetic core assembly 26, with the coils being disposed in side-by-siderelation, and separated, by solid insulating barriers, such as washertype insulating structures formed of pressboard. In this example, first,second and third groups 30, 32 and 34, respectively, of low voltagecoils, are provided, separated by first and second groups 36 and 38,respectively, of high voltage coils. The first, second and third groups30, 32 and 34-of low voltage coils are serially interconnected viaelectrical leads 40 and 42, and leads 44 and 46 at the ends of theserially connected low voltage coils connect the resulting low voltagewinding to low voltage electrical bushings sealingly disposed throughthe cover portion 48 of the tank 12. For example, lead 46 is illustratedbeing connected to the terminal on the encased end of a low voltagebushing assembly 50.

In like manner, the firstand second groups of high voltage coils areserially interconnected via an electrical lead (not shown), and the endsof the resulting high voltage winding assembly are connected to theterminals on the encased ends of high voltage bushings 52 and 54 vialeads 6 and 58, respectively. High voltage bushings 52 and 54, similarto the low voltage bushings, are sealingly disposed through the coverportion 48 of tank 12, with either the high or low voltage bushingsbeing adapted for connection to an electrical potential, depending uponwhether the transformer is of the step-up or of the step-down type.

Transformer also includes tap changer means 60, operable from outsidethe tank 12, through a suitable seal, with the tap changer means 60having a plurality of contacts connected to a plurality of tap leadsfrom the high voltage coils, such as tap leads 62, 64 and 66.

Within the winding assembly 24, stress control is achieved without lossof cooling efficiency, by. careful design of the shapes of the solidinsulating structures utilized, and controlling the width of the oilfilled cooling ducts, to prevent the potential gradient volts per mil)from exceeding the electrical breakdown strength of the solidinsulation, such as paper and pressboard, and oil filled ducts.Electrical leads outside of the winding assembly 24, such as intercoilleads 40 and 42, the intercoil leads between the high voltage groups,which are not shown, bushing leads 46,56 and 58, and tap leads 62, 64and I 66, require special attention, as the electrical stress at thethese leads, using crepe paper tape, which moves the insulation-oilinterface further from the metallic portion of the leads, to a pointwhere the voltage gradient is below the electricalbreakdown strength ofthe oil. This solid insulation is able to withstand the high electricalstresses adjacent to the metallic lead conductor, as it has a higherelectrical strength than oil, and its higher dielectric constant, i.e.,about four compared with about two for oil, reducesthe voltage dropacross the solid insulation. The thick layers of solid insulationdisposed about the electrical leads, however, trap heat generated in theleads due tothe 1 R losses, requiring more cross-section of metallicconductor in the leads than would ordinarily be required, in order toreduce the loss in the leads, and thus reduce the amount of heatgenerated therein. Increasing the number of conductive strands in alead, however, to increase the cross-sectional area of the leadstructure, increases its losses due to circulating currents, as theleads are usually located in a high leakage flux field. Elaboratetranspositions of thestrands of the lead, to reduce circulating currentmagnitudes, substantially increase the manufacturing cost of the leads.Thus, it would be desirable to reduce the potential gradient adjacent tothese leads, without increasing the manufacturing cost of the leads andwithout hindering the transfer of heat from the leads to the surroundingcooling oil.

The present invention accomplishes this objective by a structure whichreduces the potential gradient surrounding the leads to substantiallyzero, making it unnecessary to heavily tape the leads, which thusenables heat to be readily removed therefrom, and transfers the stressto an electrode surrounding and spaced from the lead, which electrode isat the electrical potential of the lead, but which carries no current.Thus, solid insulation may be applied to the electrode without regard totrapping heat, as virtually no heat is generated in the electrodestructure.

The electrode structure, according to the teachings of the invention, isan electrical conductor which has been spirally wound to provide aplurality of continuous, axially spaced conductor turns, with the insidediameter of the turns defining an opening through which an electricallead is disposed. The cooling oil is free to flow through the opening inthe electrode defined by the plurality of turns, and also through thespace between adjacent turns, enabling the lead structure to operate atabout the same temperature as the coil to which it is connected. Whilethe turns of the electrode are axially spaced, they are close enoughtogether to insure that the electrode functions as a substantiallycylindrical continuous electrode structure, which, when connected to thelead, increases the effective radius of the lead to the radius of theelectrode. The potential gradient between the lead and its surroundingelectrode is thus substantially zero, since they are at the sameelectrical potential, making it unnecessary to have more than a thinlayer of solid insulation wrapped about thelead. Heat transfer from thelead conductor to the surrounding oil is thus promoted, making itunnecessary to increase the number of conductive strands in the lead.The electrode is connected to the lead at a single point, i.e., suchthat an electrical circuit is not established through theelectrode.Since there will be no FR losses in the electrode, itmay be insulatedwith a heavy layer of solid insulation, if desired, without regard toimpeding heat transfer. Thus, the electrode not onlyreduces thepotential gradient in the oil by increasing the efiective radius of thelead, but it may include solid insulation disposed about its outersurface to take advantage of the higher electrical strength and thehigher dielectric constant of the solid insulation, such as crepe papertape, and to also space the oil even further from the conductive'portionof the electrode. FIGS. 2 through 6 illustrate different embodiments ofthe invention, using both solid and braided electrical conductor for thestress reducing electrode.

More specifically, FIG. 2 is an elevational view of the encased end 78of an electrical bushing 80 having a terminal 82 to which an electricallead 84 is electrically and mechanically secured. Bushing 80 extendsbelow the level 84 of the liquid coolant disposed in the associatedtank. Bushing 80 may be a bushing of a transformer, such as transformer10 shown in FIG. 1, for an electrical reactor, or for a circuit breaker,and it may be at a potential when energized that would require heavytaping of lead 84 in order to prevent electrical breakdown of thesurrounding oil. Instead of heavily taping lead 84, however, anelectrode is disposed in spaced relation about lead 84, and electricallyconnected thereto, as indicated schematically by lead 92. Electrode 90is formed of a metallic conductor 94, as best shown in FIG. 2, takenalong the line between arrows III-Ill. The metallic conductor of whichelectrode 90 is formed includes a plurality of spirally wound turns 96which define a circular opening 98, or elliptical opening, if desired,which opening is dimensioned to receive the electrical lead 84 andprovide a space betweenthe lead 84 and the inside diameter of opening 98for the cooling oil to flow. The spacing between the lead 84 and theinside diameter of opening 98 is maintained by spacer means, such as aplurality of insulating spacer blocks 100 and 102 which are fixedbetween predetermined turns 96 of the electrode 90 and the lead 84.

The plurality of turns 96 of electrode 90 are axially spaced from oneanother, as illustrated in FIG. 2, in order to enable the cooling oil toflow into and out of the opening between the spaced turns, as well asthrough the open ends of the electrode structure. The spacing betweenturns, however, should not be so great that the electrode ceases tofunction as a substantially continuous cylindrical electrode, as it musthave this characteristic in order to reduce the potential gradientbetween the lead 84 and electrode 90 to substantially zero, and toincrease the effective radius of the lead 84 to that of the electrode90.

The electrode 90 may be preformed, and it may have a pigtail leadconnected thereto, which is brazed to the conductive portion of lead 84,or to the terminal 82 on the encased end of bushing 80, to provide theconnection 92 between the electrode 90 and the electrical potential atwhich the lead 84 is energized. Or, the pigtail connection may beinitially connected to the electrical lead 84, and subsequentlyconnected to the electrode 90. Since only a single electrical connectionis made to electrode 90, no load current will flow therein, and .herewill be no IR losses. Thus, as illustrated in FIG. 3, a layer of solidinsulation 106 may be disposed about the outer :urface of conductor 94,which will increase the effectiveness of electrode 90, as hereinbeforeexplained.

FIG. 4 is a fragmentary view of two interconnected leads 110 and 112,which may be the leads from two coils of transformer 10, completing aseries connection between two adjacent coil groups. In this embodiment,when two leads 110 and 1 12 are to be joined, such as by brazing, it isconvenient to provide two preformed electrodes 1 l4 and 116, each ofwhich may be constructed similar to the electrode 90 shown in FIGS. 2and 3, each having a plurality of axially spaced turns formed of aninsulated electrical conductor. In preparation for making the connectionbetween leads 110 and 112, the end of each lead would be prepared forbrazing and electrodes 114 and l 16 would be placed over the leads 1 and112, respectively. The two spiralled electrodes 114 and 116 may then becompressed to provide clearance for making the braze between the twoleads. Pigtails, illustrated schematically at 110 and 120 are thenconnected from electrodes 114 and 116, respectively, to theinterconnected lead structure. A thin layer of insulating tape may bewound about the brazed connection formed between the leads, and theconnection between the leads and the pigtails, and theelectrodestructures 114 and 116 may be rigidized and spaced from theirassociated leads with insulating spacer means, as hereinbeforedescribed.

FIG. 5 illustrates a tap changer lead 130 connected between a terminal1320f a tap changer, such as the tap changer 60 shown in FIG. '1, and atap lead 134 from a coil or winding. A spiral electrode 136 having aplurality of turns 138 is disposed about lead 130 and the necessaryportions of terminal 132 and coil lead 134. A pigtail 140 is connectedfrom electrode 136 to lead 130 or to terminal 132, to energize electrode136 at the same potential as lead 130. Instead of using a solidconductor for the stress reducing electrode, it would also be suitableto use a flexible braided conductor. This embodiment of the invention isshown in FIG. 6. FIG. 6 is a fragmentary view of a lead 150 having aplurality of 'metallic conductive strands 152, formed into a coherentstructure with a thin layer 154 of insulating tape. A tubular corrugatedpressboard insulating structure 156 is disposed about lead 150, whichhas spiralled furrows 158 and ridges 160. Slots 161 are formed or cutinto ridges 160, to enable oil flow through the wall of the insulatingstructure 156. The insulating structure 156 is spaced from lead 150 by asuitable spacer means (not shown). A conductor 170 is wound about theinsulating structure 156, by placing the conductor 170 in the spiralledfurrow 158.

Conductor 170 includes a flexible, braided conductive strand portion172, with the conductive strands being woven tightly about an insulatingcore member 174. The insulating core member 174 may be formed of acellulosic insulation, such as cotton fibers, a silicon rubber, or anyother suitable insulating material. The braided or woven conductors 172include a large plurality of relatively fine metallic wires or strands.The individual wires or strands 174 are woven to provide a substantialangle between their direction and the longitudinal direction of theinsulating core member 174, allowing the conductor 170 to be easilyshaped to conform to the furrows 158 in the insulating structure 156,and it also allows the length of conductor 170 to change along with anychanges in the dimensions of structure 156 during the variousmanufacturing steps in the construction of the associated electricalpower apparatus.

While. the diameter of the strands 172 is not critical, the diametershould be selected to be as small as practical. Very small or finediameter strands provide a substantially smooth outer surface on theresulting woven conductor, which is necessary in order to reduce thepotential gradient at its surface. Very fine strands are also desirablebecause they are individually so flexible that any broken ends that mayextend outwardly from the surface of the woven conductor will be bentinwardly to conform to the surface of the conductor when the conductoris insulated, such as with a layer 176 of paper insulation, asillustrated in FIG. 6. Small diameter strands also aid the structureelectrically, as reducing the diameter of the strands increases theirresistance to the flow of eddy currents, produced when the electrode issubjected to a high leakage field. Copper strands, each having adiameter of 0.0063 inches are suitable for the woven conductor, butother diameters and other metals, such as aluminum, stainless steel, andthe like, may be used.

In summary, there has been disclosed new and improved electrical powerapparatus having a casing filled with a fluid coolant, such as mineraloil, and having at least one electrical lead disposed in the tank whichis immersed in the coolant and which is at an elevated electricalpotential when the power apparatus is energized. The electrical lead issurrounded with an electrode which is connected to the lead, reducingthe potential gradient between the electrode and lead to substantiallyzero, and increasing the effective radius of the lead to the radius ofthe surrounding electrode. The electrode is formed of an electricalconductor having a plurality of axially spaced turns, and the insidediameter of the turns is spaced from the electrical lead. Thus, thecoolant may flow adjacent to the lead, through the openings at the endsof the electrode, and also between the turns of the electrode. Sincethere is little potential gradient adjacent to the lead surface, it needhave only a thin layer of insulating tape. Thus, the oil flowing overits surface will efficiently remove heat therefrom. Since the electrodedoes not carry load current, it may be insulated to increase itseffectiveness, as the insulation will not impede the transfer of anyheat. In addition to effectively reducing the potential gradientadjacent an electrical lead, and promoting heat transfer from the lead,the lead structure need not be modified by addition additionalconductive strands thereto, which strands may increase the losses in thelead due to circulating currents, and the stress reducing structuretaught by the invention may be manufactured for a relatively low cost,and quickly and easily assembled with an associated lead structure atthe time of manufacturing the associated electrical power apparatus.

We claim as our invention: 1. Electrical power apparatus adapted forenergization by a source of electrical potential, comprising:

a casing, fluid cooling means disposed in said casing, at least oneelectrical lead disposed in said casing and immersed in said fluidcooling means, said at least one electrical lead being at an elevatedelectrical potential when the electrical power apparatus is energized,an electrode, including an electrically conductive member having aplurality of continuous, axially spaced turns, defining a predeterminedopening through the electrode, said at least one electrical leadextending through the predetermined opening in said electrode, spacermeans disposed to space said at least one electrical lead from the turnsof said electrode, and means interconnecting said at least oneelectrical lead and said electrode, to increase the efi'ective radius ofsaid at least one electrical lead and reduce the potential gradientsurrounding said at least one electrical lead,

while enabling free flow of said fluid cooling means adjacent to said atleast one electrical lead.

2. The electrical power apparatus ofclaim 1 wherein the at least oneelectrical lead includes electrical conductor means having insulatingmeans disposed about the outer surface of the electrical conductormeans. I

3. The electrical power apparatus of claim 2 wherein the electrodedisposed about them least one electrical lead includes insulating meansdisposed about the outer surface of its turns.

4. The electrical power apparatus of claim 1 wherein the electrodedisposed about the at least one electrical lead includes insulatingmeans disposed about the outer surface of its turns.

5. The electrical power apparatus of claim 1 including an insulatingbushing sealingly disposed through the casing with the at least oneelectrical lead being connected to said insulating bushing.

6. The electrical apparatus of claim 1 including an electrical windingand a tap changer disposed within the casing, with the at least oneelectrical lead interconnecting said electrical winding and said tapchanger.

7. The electrical apparatus of claim 1 including an electrical windinghaving a plurality of spaced coils disposed in the casing, and the atleast one electrical lead interconnects two of said plurality of spacedcoils.

8. The electrical apparatus of claim 1 wherein the spacer means includesa corrugated tubular insulating member having spirally disposed furrowsand ridges, with the turns of the electrode being disposed in thefurrows, and including slots formed in the ridges to promote circulationof the fluid cooling means adjacent to the at least one electrical lead.

9. The electrical power apparatus of claim 8 wherein the electrodeincludes a plurality of electrically conductive strands woven togetherabout an insulating core member.

10. The electrical apparatus of claim 1 wherein the electrode includes aplurality of electrically conductive strands woven together about aninsulating core member.

11. The. electrical power apparatus of claim 1 wherein the electrode hasa solid metallic cross-section, and insulating means disposed about theouter surface of the solid metallic member.

12. The electrical power apparatus of claim 1 wherein the fluid coolingmeans is mineral oil.

13. The electrical power apparatus of claim 1 including at least twoelectrical coils, with the at least one electrical lead including an endof each coil, and means interconnecting the ends of the coils, andincluding a second electrode having a plurality of turns defining anopening, with the at least one electrical lead also extending throughthe opening in the second electrode, and including means connecting thesecond electrode to the at least one electrical lead.

14. The electrical power apparatus of claim 1 wherein the meansinterconnecting the at least one electrical lead and the electrodecontacts only a single turn of the electrode, to maintain the electrodeat the potential of the at least one lead without heating the electrodedue to current flow.

1. Electrical power apparatus adapted for energization by a source ofelectrical potential, comprising: a casing, fluid cooling means disposedin said casing, at least one electrical lead disposed in said casing andimmersed in said fluid cooling means, said at least one electrical leadbeing at an elevated electrical potential when the electrical powerapparatus is energized, an electrode, including an electricallyconductive member having a plurality of continuous, axially spacedturns, defining a predetermined opening through the electrode, said atleast one electrical lead extending through the predetermined opening insaid electrode, spacer means disposed to space said at least oneelectrical lead from the turns of said electrode, and meansinterconnecting said at least one electrical lead and said electrode, toincrease the effective radius of said at least one electrical lead andreduce the potential gradient surrounding said at least one electricallead, while enabling free flow of said fluid cooling means adjacent tosaid at least one electrical lead.
 2. The electrical power apparatus ofclaim 1 wherein the at least one electrical lead includes electricalconductor means having insulating means disposed about the outer surfaceof the electrical conductor means.
 3. The electrical power apparatus ofclaim 2 wherein the electrode disposed about the at least one electricallead includes insulating means disposed about the outer surface of itsturns.
 4. The electrical power apparatus of claim 1 wherein theelectrode disposed about the at least one electrical lead includesinsulating means disposed about the outer surface of its turns.
 5. Theelectrical power apparatus of claim 1 including an insulating bushingsealingly disposed through the casing, with the at least one electricallead being connected to said insulating bushing.
 6. The electricalapparatus of claim 1 including an electrical winding and a tap changerdisposed within the casing, with the at least one electrical leadinterconnecting said electrical winding and said tap changer.
 7. Theelectrical apparatus of claim 1 including an electrical winding having aplurality of spaced coils disposed in the casing, and the at least oneelectrical lead interconnects two of said plurality of spaced coils. 8.The electrical apparatus of claim 1 wherein the spacer means includes acorrugated tubular insulating member having spirally disposed furrowsand ridges, with the turns of the electrode being disposed in thefurrows, and including slots formed in the ridges to promote circulationof the fluid cooling means adjacent to the at least one eLectrical lead.9. The electrical power apparatus of claim 8 wherein the electrodeincludes a plurality of electrically conductive strands woven togetherabout an insulating core member.
 10. The electrical apparatus of claim 1wherein the electrode includes a plurality of electrically conductivestrands woven together about an insulating core member.
 11. Theelectrical power apparatus of claim 1 wherein the electrode has a solidmetallic cross-section, and insulating means disposed about the outersurface of the solid metallic member.
 12. The electrical power apparatusof claim 1 wherein the fluid cooling means is mineral oil.
 13. Theelectrical power apparatus of claim 1 including at least two electricalcoils, with the at least one electrical lead including an end of eachcoil, and means interconnecting the ends of the coils, and including asecond electrode having a plurality of turns defining an opening, withthe at least one electrical lead also extending through the opening inthe second electrode, and including means connecting the secondelectrode to the at least one electrical lead.
 14. The electrical powerapparatus of claim 1 wherein the means interconnecting the at least oneelectrical lead and the electrode contacts only a single turn of theelectrode, to maintain the electrode at the potential of the at leastone lead without heating the electrode due to current flow.